The present invention relates to an improvement made to plants used for treating sheet materials using pressurized water jets, which act on the substance in the manner of needles, and which are used in particular for treating nonwoven structures for the purpose of giving them cohesion and/or modifying their appearance.
Such a technique, which has been used for decades, as is apparent for example from patents U.S. Pat. Nos. 3,214,819 and 3,485,706, consists in subjecting the sheet structure to the action of water jets coming from one or more successive injector rails, the sheet or web being supported by a porous or perforated conveyor belt or rotating roll, subjected to a suction source allowing the water to be recovered.
One of the essential elements of such plants is the system for forming the water jets or needles, commonly referred to by the term xe2x80x9cinjectorxe2x80x9d.
The invention relates more particularly to a novel type of perforated plate comprising such injectors and which are one of the essential elements for forming water jets or needles.
The injectors used at the present time have a general structure as illustrated in FIG. 9 of patent U.S. Pat. No. 3,508,308 and U.S. Pat. No. 3,613,999.
More recently, EP 400249 (corresponding to U.S. Pat. No. 5,054,349) proposed an improved injector which not only makes it possible to inject water at a very high pressure (greater than 100 bar) but has a structure such that it allows the perforated plate, through which the microjets pass, to be easily fitted and removed, for example for the purpose of cleaning.
The appended FIG. 1 illustrates, in a general way, the structure of an injector.
Referring to this figure, such an assembly is therefore in the form of a continuous injector rail which extends transversely with respect to the direction of movement of the sheet material (F) to be treated, for example a nonwoven, and the length of which is matched to the width of said material.
This injector rail consists of a main body (1) which can withstand any deformation due to the water pressure, and in the upper part of which there is a chamber (2), in general of cylindrical shape, fed with pressurized water by a pump (not shown) through pipework (3).
Placed inside the chamber (2) is a cartridge (4) consisting, for example, of a perforated cylinder lined with a filter cloth, which not only acts as a filter, but also as a distributor.
The pressurized water introduced inside the chamber (2) then flows through cylindrical holes (5), which are separated with a regular pitch over the entire width of the injector, the diameter of which holes is in general between 4 mm and 10 mm, the thickness of the wall between two consecutive holes being about 3 to 5 mm.
These cylindrical holes (5), the outlet end of which may possibly be of conical shape, then emerge in a lower chamber (6) at the base of which a plate (7) provided with microperforations is positioned, the diameter of which may be between 50 and 500 xcexcm and preferably between 100 and 200 xcexcm, enabling water jets or needles (8) to be formed which act directly against the surface of the material (F) to be treated, for example a nonwoven web.
The perforated plate (7) is held against the main body of the injector, according to the teachings of EP 400249, for example, by longitudinal jaws (9) subjected to the action of hydraulic cylinders which allow a clamping action to be exerted by means of a system of cross bars and pull rods placed along the injector.
A seal (not shown) is placed between the perforated plate (7) and the base of the main body (1).
At present, the perforated plates (7) which enable the jets to be produced are all made by drilling or punching thin strips of stainless steel.
These strips have a thickness of between 0.6 and 1.2 mm.
FIG. 2 is a sectional view of a perforated plate used at present.
In such plates, the capillaries (10) enabling jets to be formed are, as mentioned above, obtained by drilling or punching and have a general shape such that they comprise, if the direction of movement of the jets is followed, a cylindrical inlet region (11) extended by a divergent wall.
While such plates are satisfactory when the pressure of water in the injector is less than 200 bar, they do not however operate industrially at pressures which are higher so as to obtain a high fluid velocity which could reach 300 m/sec.
This is because it has been noticed that the mean life of such perforated plates made of stainless steel does not exceed 24 hours when working at pressures of 400 bar.
Moreover, the drilling and punching techniques used to produce the capillaries do not allow a perfect surface condition of the inner wall to be obtained or a sharp edge to be produced at the inlet of each capillary in an accurate and regular way which, at high fluid velocities, leads to a deterioration in the quality of the jets by the formation of turbulence in the flow.
A novel type of perforated plate has now been found and it is this which forms the subject of the present invention, which makes it possible to solve the aforementioned problems and allows water to be supplied at high pressure, which could reach 400 bar or more, without damaging said plate after a period of use which could reach several hundred hours.
Moreover, the novel type of plate according to the invention makes it possible to obtain jets having a high velocity which can reach 300 m/sec or even more, with very high homogeneity and regularity over the entire length of the plate.
In addition, it has been noted that, compared to the prior art, the jets obtained with the plate according to the invention remain coherent over a greater length.
In general, the invention therefore relates to a device called an xe2x80x9cinjectorxe2x80x9d allowing sheet material (nonwoven, textile complex, film, paper, etc.) to be treated by means of water jets/needles, which comprises:
a body for supplying pressurized water, comprising a feed chamber extending over the entire length of said body, and inside which the pressurized water is taken through a filter;
a distribution region, distributing the pressurized water over the entire treatment width, comprising a plate fitted with microperforations, the holes of which define water needles directed against the surface of the material to be treated, and it is characterized in that microperforations or capillaries are produced inside inserts made of hard materials of the type comprising zirconia, ruby, sapphire, ceramic and other materials of equivalent hardness, set inside holes previously made over the entire thickness of the plate.
According to one embodiment, the inserts preferably have a thickness less then the depth of the holes made in the plate.
Moreover, although said inserts can be placed in a single row over the entire length of the plate, it is possible to place them in two parallel rows, the capillaries or microperforations being offset with respect to each other from one row to the next.
The capillary or microperforation of each insert comprises a cylindrical inlet region, the diameter of which is between 50 and 500 xcexcm and preferably between 100 and 200 xcexcm as for the microperforations of the prior art plates. This cylindrical part may be extended by a divergent region in the form of a dome or a cone or by a sudden widening obtained by means of an outlet region of greater diameter than the inlet region.
Advantageously, the thickness of the plate will be between 1 and 3 mm, the machined holes inside which the insert are set having, themselves, a diameter between 0.5 and 2 mm.
The lower face of the inserts may be located recessed with respect to the lower face of the plate.
Using such a design for the perforated plate, it is possible to generate jets which are equivalent in number and in diameter to those of the plates belonging to the prior art with the advantage of forming each jet in a nozzle whose geometry, surface condition and hardness are exceptional.
Apart from an increased life, these new perforated plates with inserts made of zirconia, sapphire, ruby or other materials of equivalent hardness, such as ceramic, allow operation at high pressures, while having very good regularity of jets with an increased life for the plates and moreover, and surprisingly, such plates lead to an improvement in the strength of the products obtained, when treating nonwovens.